The physics teacher at Earl Haig Secondary School in Ontario Canada did a great activity with catapult models. Check out the video!

Catapults were awesome weapons originally invented in Greek and Roman Times. They can take many forms and we have made two kits, one using the power of torsion stored in twisted rope, and the other using the power of tension, stored in bamboo tensioners. Catapults also had slings attached to them, in which case they became onagers.